linux-kernel - Re: [linux-next:master] [x86/module] 6661cae1aa: WARNING:at_arch/x86/mm/pat/set_memory.c:#__cpa_process

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Message-ID: <Zw08TviEUyTpy8N5@kernel.org>
Date: Mon, 14 Oct 2024 18:44:14 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: kernel test robot <oliver.sang@...el.com>, oe-lkp@...ts.linux.dev,
	lkp@...el.com, Linux Memory Management List <linux-mm@...ck.org>,
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Subject: Re: [linux-next:master] [x86/module] 6661cae1aa:
 WARNING:at_arch/x86/mm/pat/set_memory.c:#__cpa_process_fault

On Mon, Oct 14, 2024 at 08:27:36AM -0700, Dave Hansen wrote:
> On 10/13/24 01:17, Mike Rapoport wrote:
> > On Fri, Oct 11, 2024 at 09:30:33AM -0700, Dave Hansen wrote:
> >> On 10/11/24 08:40, Mike Rapoport wrote:
> >>> On Fri, Oct 11, 2024 at 07:00:01AM -0700, Dave Hansen wrote:
> >>>> On 10/11/24 06:08, Mike Rapoport wrote:
> >>>>> This patch disables ROX caches on 32-bit, it should fix the issue.
> >>>> While I'm not going to shed a tear for 32-bit, what's the actual
> >>>> compatibility issue with 32-bit?
> >>> From the stack trace it looks like execmem tries to update the direct map
> >>> for highmem memory, and cpa is not happy about it.
> >>
> >> First of all, if it's a highmem problem, shouldn't the check be for
> >> CONFIG_HIGHMEM and not on 32-bit vs. 64-bit?  We do have non-highmem
> >> 32-bit configs.
> > 
> > 32 bit also does not have ARCH_HUGE_VMALLOC and execmem cache will be
> > anyway populated with 4k pages, so I don't see why it would be useful on 32
> > bit all.
> 
> It's not really about making it _available_ to 32-bit, but making sure
> that we're actually doing the check against the right feature and in the
> right way.
> 
> To me, it seems like execmem itself should be excluding all HIGHMEM=y
> builds or _maybe_ all 32-bit builds because execmem has the built-in
> assumption that vmalloc memory is in the direct map.

I presume you mean execmem cache here, as execmem in general should work
everywhere.

After discussion with Christoph about how to define
execmem_fill_trapping_insns(), I'm going to add a Kconfig opt-in option
that will guard the entire execmem cache implementation and have it
selected by x86_64.
 
-- 
Sincerely yours,
Mike.